Acoustic design of water features for the built environment

Due to their inherent positive quality and sound masking properties, water generated sounds are very popular in the context of soundscape design. This paper examines the acoustic properties of waterfalls, cascades and fountains tested in the laboratory under controlled conditions. The study was developed in view of characterising the impact of design factors on the acoustics of small to medium sized water features which can be installed in a variety of outdoor and indoor spaces. The laboratory approach ensured an accurate and reliable analysis of water generated sounds, and the flexible structure used for the research allowed testing a wide range of design factors such as flow rate, source’s height, waterfall’s width, waterfall’s edge design and impact material. Results show that LAeq increases logarithmically with flow rate for most of the designs tested. Furthermore, larger sound pressure levels can be obtained by generating vibrating bubbles; this can be done by distributing the same amount of water over several streams, as well as by using water as an impact material rather than solid surfaces. Comparisons with road traffic noise predictions also show that there is a mismatch between the frequency responses of traffic noise and water sounds, with the exception of waterfalls with large flow rates that can generate low frequencies comparable to those of traffic noise.